Small or utility internal combustion engines are used to power a variety of various products including lawn and garden products such as chain saws, lawn mowers, edgers, grass and weed string trimmers, leaf air blowers and the like. Many of these engines are single cylinder two-cycle or four-cycle spark ignited gasoline powered internal combustion engines having a carburetor or other device supplying a gasoline fuel and air mixture to the combustion chamber of the operating engine. The ratio of air-to-fuel of the fuel mixture may be calibrated for a particular engine or a particular product but different engine operating characteristics such as varying loads during use of the product, type of fuel, altitude, condition of the air filter and/or differences among engines and/or components in a production run may adversely affect engine operation and performance. To improve engine performance and operation under a variety of these and other conditions, some engines include a control system and process which throughout essentially every period of engine continuous operation repeatedly and substantially continuously tests and determines whether a proper air-to-fuel ratio of the fuel mixture is being supplied to the engine and, if not, changes the air-to-fuel ratio of the supplied fuel mixture to improve engine operation and performance and often to control exhaust emissions to comply with Governmental regulations.
One such system and method which essentially continuously tests and if need be changes the ratio of air-to-fuel of a fuel mixture it delivers to an operating engine is disclosed in U.S. patent application Ser. No. 14/773,993, filed Sep. 9, 2015, the disclosure of which is incorporated herein by reference in its entirety. In this method, the engine operating speed is sensed and determined, an air-to-fuel ratio of a fuel mixture delivered to the operating engine is changed and preferably enleaned, and a second engine speed is sensed and determined after at least some and preferably near the end of the changed air-to-fuel ratio event. Based at least in part on the difference between the first and second engine speeds, it is determined whether a change in the air-to-fuel ratio of the fuel mixture supplied to the engine is needed or desired and, if so, a change in the air-to-fuel ratio of the fuel mixture delivered to the engine is implemented. Developing such a control system and method which is always trying to automatically sense and adjust the air-to-fuel ratio of the operating engine in the field or essentially continuously during the entire time period of each engine operation can be difficult and requires relatively complex programming in order to essentially eliminate the risk of erroneous automatic self-adjustment events which may be initiated by unforeseen engine operating conditions.